Use 05AF-2121 Bottle Cap Plug to seal the third “tapered” luer hole. Or, use 05AF-2141 Plug to seal unused 1/16” or 1/8” bottle cap holes. Alternatively, try 05AF-2131 or 05AF-2151 Filter Bottle Cap Plug for an extra cap hole. The 20µm SS frit prevents foreign matter from contaminating solvent while leaving the bottle open to the atmosphere, thus allowing fluid to be pulled out without creating a vacuum.